Medical devices can be implanted in the bodies of patients for various purposes. Some medical devices detect physiologic events and may apply therapy in response to certain events of interest. For example, a cardiac pacemaker can detect a lull in the beating of the patient's heart and apply an electrical pulse to stimulate the heart into beating again. Other devices may be implanted, such as defibrillators, neuro-stimulators, ICDs, CRTS, drug pumps, and various types of sensors. It is becoming more common to implant multiple devices in a single patient. In such situations, a controller device can communicate with the implanted medical devices. The medical devices can communicate data to the controller in response to commands from the controller. When multiple medical devices are implanted, the controller must be able to direct commands to a selected device with a relatively high degree of reliability.
Conventionally, globally unique identifiers, such as device manufacturing serial numbers, have been used to identify an implanted electronic device during communication with diagnostic and control equipment outside a patient's body. Typical systems involve a single external master controlling communication with a single slave device within the body. Multiple devices within a body in communication with each other or with an external device require using globally unique identifiers as well, but this can unnecessarily burden the local communication traffic.
The representation, in bits, of a globally unique identifier must be sufficiently large to identify a global population of devices. For example, 20- to 64-bit globally unique identifiers are common for electronic devices. In a local patient environment that can consist of approximately 6 implanted devices in communication with each other or with a local device external to the body, transferring large, unique identifiers during communication sessions represents communication overhead that consumes power and delays transfer of desired data within the local environment.